Thank you for your question regarding grounding via lightning protection systems. It is our pleasure to help.
Every known standard from the NFPA 70 National Electrical Code (NEC) to the NFPA 780 Lightning Protection Code to IEEE standards and more, all require that every single system within the facility be bonded to a common ground source. This means that the lightning protection system and the electrical grounding system must be bonded together at some point. However, we must remember that there are several systems in play that must be accounted for. The NEC has a requirement for a dedicated low-impedance fault current path back to the first service disconnect to ensure that the Over Current Protection Devices (OCPD) such as circuit breakers and fuses will function properly. This requirement is separate and independent from the requirements of the NFPA lightning Protection system. Using the lightning protection system for this path is not allowed.
NEC Articles 250.60 & 250.106 are the only two sections in the NEC that discuss grounding and lightning protections systems, which isn’t much. The thing to remember, is that these are separate systems governed under separate codes. While the lightning protection system must be bonded to the electrical system ground at the main service disconnect, you don’t want to use it as part of the electrical system. Mostly to protect the electrical system itself from the lightning. The lightning protection system is designed to provide a direct path to earth for lightning strikes to travel on. If your switch gear is in that path, then it will become damaged during a strike. Bottom line, you must provide a ground fault path back to the first service disconnect that is separate from the lightning protection system.
Also, you should avoid using dissimilar metals when bonding. Tin and copper will tend to corrode, you would be much better served if you were to use brass fittings when bonding to copper. Here is a previous post that discusses corrosion issues:
We hope you find this information useful, if you should have any further questions, please do not hesitate to contact us again in the future.
The Engineering Team at E&S Grounding Solutions
Photo credit: E&S Grounding Solutions